Electron beam duplication lithography method

ABSTRACT

An electron beam duplication lithography apparatus and method for focusing electrons emitted from a mask plate as a result of an application of an electric field between a mask plate and a duplication plate. Irradiation of electrons from the mask plate is assisted through an electric field lens or magnetic field lens, or a combination thereof from an electron field emission material formed into a pattern on a flat surface of a substrate. The result is that a congruent or similar pattern is lithographed by electron beam exposure onto an electron beam resist film from a field emission film having the congruent or similar pattern to be created.

TECHNICAL FIELD

The present invention relates in general to electron beam duplicationlithography.

BACKGROUND INFORMATION

Referring to FIG. 4, there is illustrated a prior art apparatus forperforming electron beam duplication lithography using a photo cathode.A quartz substrate 41 forms the base of a mask plate 40 on which achromium (Cr) light shield pattern 42 is formed. On the surface ofsubstrate 41 and between the portions of the Cr light shield pattern 42,a photo cathode film 43 is deposited in a defined pattern. The photocathode material 43 emits electrons when bombarded by light energy, suchas ultra violet light 46. An exemplary photo cathode material is cesiumiodide (CsI), which is a low work function material. An ultra violetlight source (not shown) irradiates ultra violet light 46 through thebackside of quartz substrate 41, bombarding the photo cathode film 43,resulting in a secondary emission of electrons 47 from the photo cathodepatterned film 43. The emitted photo electrons 47 are accelerated by anelectric field applied by acceleration electric source E, and may befocused into an electron beam 47 by a focusing magnetic field. (magneticfield lens) 48 created by magnetic coils (not shown), onto electron beamresist film 45 deposited on substrate plate 44. In this manner, the“lithography” is not created by light but by exposure of the resist film45 to an electron beam The result is that the pattern formed by lightshield pattern 42 and photo cathode film 43 is duplicated when portionsof resist film 45 are bombarded by the electron beams 47. The electronbeams change the molecular structure of the resist such that the portionof the resist bombarded by electrons is easy to dissolve in specificchemicals for the resist (“developer” chemicals).

However, there are several disadvantages to the prior art techniqueillustrated in FIG. 4. Because the mask plate is itself a passive lightemission device using a photo cathode, there is a need for an ultraviolet lamp. Furthermore, the wave length of ultra violet light islimited to about 0.1 micrometers (μm), and thus, duplication lithographybelow 0.1 micrometers is very difficult, if not impossible.Additionally, the lifetime of the photo electron plane is limited to aduplication cycle of approximately 50 cycles when using CsI for thephoto electron plane. Moreover, although the quartz substrate 41 isquite conductive to ultra violet light, quartz is a relatively expensivematerial especially in large areas.

Furthermore, it is difficult to achieve a duplication that is preciselyone-to-one between the pattern to be duplicated and the pattern that iscreated, without molding the surface of the photo cathode pattern 43 tobe concave, which will result in surface roughness on the concavesurface and a duplication that is even still difficult to produce in aone-by-one manner.

SUMMARY OF THE INVENTION

The present invention addressed the foregoing needs by an electron beamduplication lithography apparatus utilizing a field emission cathode foremitting electrons to the electron beam resist film. One advantage ofthe present invention is that duplication lithography of a fine patternwith features below 0.1 micrometers is possible. Another advantage ofthe present invention is that a high duplication directivity ofone-by-one is achievable. Yet another advantage of the present inventionis that it does not require an ultra violet light source, nor a quartzsubstrate.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter which form the subject of the claims of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates an electron beam duplication lithography apparatusconfigured in accordance with an embodiment of the present invention;

FIG. 2 illustrates an exemplary duplicated pattern created by anembodiment of the present invention;

FIGS. 3A, 3B, and 3C illustrate an alternative embodiment of the presentinvention;

FIG. 4 illustrates a prior art electron beam duplication lithographyapparatus; and

FIGS. 5A-5L illustrate a process for creating a mask plate in accordancewith the present invention.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth toprovide a thorough understanding of the present invention. However, itwill be obvious to those skilled in the art that the present inventionmay be practiced without such specific details.

Refer now to the drawings wherein depicted elements are not necessarilyshown to scale and wherein like or similar elements are designated bythe same reference numeral through the several views.

In solving needs of the prior art, the present invention provides anelectron beam duplication lithography apparatus and method for focusingelectrons emitted from a mask plate as a result of an application of anelectric field between a mask plate and a duplication plate. Irradiationof electrons from the mask plate is assisted through an electric fieldlens or magnetic field lens, or a combination thereof from an electronfield emission material formed into a pattern on a flat surface of asubstrate. The result is that a congruent or similar pattern islithographed by electron beam exposure onto an electron beam resist filmfrom a field emission film having the congruent or similar pattern to becreated.

Because there is no use of a photo cathode, it is possible to realize alonger lifetime of the mask plate. Moreover, it is possible to constructthe mask plate using a conductive substrate or having a conductive filmcoated glass substrate or ceramic substrate or a metal substrate, at alower cost. Moreover, it is possible to achieve higher current densitieswith a field emitter, resulting in a lessening of the exposure time ofthe resist film, resulting in a faster lithography process, which willincrease the manufacturing throughput.

Because the mask plate surface is flat, it is possible to moreeffectively duplicate in a one-to-one manner, plus there is no inherentlimit to the size of the cathode. The whole pattern can be exposed inparts of it at a time. It is also possible to realize more preciseduplication lithography below the 0.1 micrometer level.

A field emission device can use low work function materials, such as adiamond-like carbon thin film. As a result, the two plates can bepositioned closer together resulting in higher current densities,resulting in the increased efficiency, all without a degradation of themask plate, since the diamond-like carbon thin film is more resistant todamage over its lifetime.

Referring to FIG. 1, there is illustrated a cross-section view of anelectron beam duplication lithography apparatus in accordance with anembodiment of the present invention. The apparatus may be operated in avacuum chamber. The mask plate 10 is a cathode using a substrate 11 withan electron emission device 12 formed in a predetermined pattern on thesubstrate 11. The substrate 11 could be made from a conductive filmcoated glass, ceramics, silicon, metal, etc. The electron emissionmaterial 12 can be diamond-like carbon (DLC) film, diamond film, carbonfilm, carbon nanotube (CNT) film, porous silicon film, or any otherfield emission material. Furthermore, though the surface of the materialis relatively flat, the present invention should not be limited toexclude micro-tip and other projection-like features of the fieldemission material. In this example, electron beams 15 emit from theplural patterned field emission devices 12 connected to the cathodeelectrode, and are focused to irradiate onto electron beam resist film14 on duplicated plate 13. In one exemplary embodiment of the presentinvention, the mask plate 10 and the duplicated plate are in parallelwith each other and separated between 50 micrometers and fivemillimeters apart. The substrates 11 and 13 may be conductive, orconductive films may be deposited thereon in order that an exemplaryapplied voltage from one kilovolt to ten kilovolts can be provided forpromotion of emission of electrons from the electron emission device 12toward the electron beam resist film 14. A magnetic lens (focusingmagnetic field) 16 is formed parallel to the electron beams 15 to focusthe electron beams 15 as they are irradiated toward the electron beamresist film 14. The magnetic field 16 may be created by any well knownmeans. The magnitude of the magnetic field may be a function of the gapbetween the two plates and the field strength of the electrical field.

The result of the apparatus in FIG. 1 is that an electron emission typeplate is provided that is self-emitting of electrons and the fieldemission device 12 is planar and patterned to thereby etch a duplicatedpattern into the electron beam resist film 14.

As noted, to assist in preventing spreading of emitted electrons, theelectron beam 15 can be focused with a magnetic field 16, but it is alsopossible to use an electric field lens. Also, some type of gridelectrode can also be utilized to focus the electron beams 15. Further,it is possible to have a better defined pattern into the electron beamresist material 15 by placing the plates closer together, which can alsoresult in a lowering of the voltage needed to create the accelerationvoltage E. In this case, if needed, exposure of the resist film 14 onsubstrate 13 can be formed in sections over the entire substratesurface.

FIG. 2 illustrates an exemplary duplicated pattern lithographed inaccordance with an embodiment of the present invention by electron beamduplication lithography, such as using the apparatus illustrated inFIG. 1. On the duplicated plate 21 is a pattern 22 where the resistmaterial 14 has been patterned by electron beam lithography from anelectric field emission device 12. Such electric field emission device12 will have the same pattern as the keyhole pattern 22 shown in FIG. 2.In FIG. 2, the exemplary duplicated pattern 22 is arranged in an array,but a more complex shaped pattern is possible using the presentinvention. Furthermore, inner circuitry can be formed different fromcircuitry around the periphery of the plate 21.

The lithograph time t is defined by the emission current density J andthe sensitivity S of the electron beam resist material used 14 asfollows:t=S/J

For example, when J is equal to 10 mA/cm², and the electron beam resistmaterial 14 has a sensitivity of 10 to 100 micro-Coulombs/cm², for aone-to-one duplication lithography, it is possible to perform such aprocess in 10 milliseconds.

FIGS. 3A, 3B, and 3C show cross-sections of alternative embodiments ofthe mask plate 10 shown in FIG. 1. The exemplary mask plate illustratedin FIG. 3A shows that the patterned field emission material 32 a isformed with a dielectric or conducive material 33 a onto substrate 31 awhere the surfaces of layers 32 a and 33 a are substantially coplanar.In FIG. 3B, the patterned field emission material 32 b is recessed sothat its top surface is lower than the top surface of the dielectric orconductive material 33 b.

In FIG. 3C, the field emission material 32 c is patterned onto substrate31 c, and the dielectric or conductive material is then coated inbetween the patterned field emission material 32 c and over its edges tocover the edged portions of the electric field emission device 32 c.Note, it is also possible to merely coat a single layer of fieldemission material 32 c onto substrate 31 c, and then to realize theeffective pattern of the field emission from gaps through the dielectricor conductive material 33 c.

The buried layers 33 a, 33 b, and 33 c function to assist byconcentrating the electrons emitted from the field emission materialbecause the sidewalls are at least coated by the conductive ordielectric material. The reason is that otherwise, the edges of thefield emission devices 32 a, 32 b, and 32 c will more readily yieldelectron emissions resulting in a corresponding decrease in electronemissions from the non-edged portions. This may result in non-uniformityof the emission of electrons. However, with the methods illustrated inFIGS. 3A, 3B and 3C, it is possible to suppress the irregularlithography by realizing an improvement in the uniform emission ofelectrons from the entire field emission material that is unexposed.

With the electron beam lithography of the present invention, it ispossible to realize high resolution lithography, lithography of apattern having features below 0.1 micrometers, and improved productivitywith a quicker lithography process, and a focus depth of +/−15micrometers.

Referring to FIGS. 5A-5L there is illustrated a process for creating amask plate, such as the mask plates illustrated in FIGS. 1 and 3A-3C. InFIG. 5A, a substrate 51 is provided. In FIG. 5B, an indium tin oxide(ITO) layer 52 is deposited onto substrate 51. In FIG. 5C, a fieldemitter material 53 is deposited onto the ITO layer 52. In FIG. 5D, anelectron-beam sensitive or photosensitive resist layer 54 is depositedonto the field emitter layer 53. In FIG. 5E, the resist material 54 isexposed by an E-beam or light with pattern and developed to form apatterned layer of resist 54. Note, an alternative approach may be todeposit a hard-mask layer on top of the field emitter material 53, thendeposit the resist material, then expose the resist material thendevelop it to then etch the hard-mask layer. The resist is then removedleaving a structure that is the same as above, except that the top layeris a hard-mask layer and not a resist material. Such a hard-mask layercould be used to withstand a harsh etch of oxygen plasma.

In FIG. 5F the field emitter material 53 is etched in oxygen plasma. InFIG. 5G, the resist material (or hand-mask layer) 54 is removed. In FIG.5H, a layer of silicon dioxide (SiO₂) is deposited on top of the fieldemitter 53 and ITO 52 layers. In FIG. 51, an E-beam sensitive resistlayer 56 is deposited onto the silicon dioxide layer 55. In FIG. 5J, theE-beam resist layer 56 is pattern exposed to an electron beam, developedand patterned using standard techniques in the photo mask industry. InFIG. 5K, the silicon dioxide layer 56 is etched using fluorocarbonplasma dry etch technology. In this case, line and space width isdependent on the required width. In FIG. 5L, the resist layer 56 isremoved.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims.

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 10. A method forperforming duplication lithography, comprising the steps of: providing afirst substrate with a field emitter deposited on the first substrate ina predefined pattern; providing a second substrate positioned a distancefrom the first substrate with an electron beam resist layer deposited onthe second substrate; and establishing an electric field to therebycause an emission of electron beams from substantially all of the fieldemitter towards the electron beam resist layer in order to modify theelectron beam resist layer in a pattern substantially identical to thepredefined pattern.
 11. The method as recited in claim 10, furthercomprising positioning a magnetic field lens to focus the electron beamsas they are emitted from the field emitter towards the electron beamresist layer.
 12. The method as recited in claim 10, further comprisingpositioning an electric field lens to focus the electron beams as theyare emitted from the field emitter towards the electron beam resistlayer.
 13. The method as recited in claim 10, wherein a conductive layeris positioned between the first substrate and the field emitter.
 14. Themethod as recited in claim 10, wherein a conductive layer is positionedbetween the second substrate and the electron beam resist layer.